Caries and periodontal diseases are two of the most common chronic infectious diseases affecting humankind and are always associated with dental plaque formed as a biofilm on tooth surfaces. Dental plaque is produced by sequential attachment of a variety of bacteria, which is dependent on both the species involved and the surface composition. Actinomyces naeslundii (A. naeslundii) are Gram-positive, rod-shaped bacteria that are among the first species to occupy the oral cavity and colonize the tooth's surface. A. naeslundii have been implicated in periodontal disease and root caries.
Quorum sensing is a means of intercellular communication between bacterial cells that allows bacteria to control gene expression and respond to population density as a group. Bacteria occupying the oral cavity, including A. naeslundii, use quorum-sensing systems to regulate several physiological processes, including the incorporation of foreign DNA, acid tolerance, biofilm formation, and virulence. Thus, through quorum sensing, A. naeslundii can optimize their physiology to adapt to environmental stimuli and can behave as a collective, thereby resulting in better colonization of hosts, evolution as a species, and improved responses to mechanical, physical, and chemical stresses. Consequently, bacteria in biofilms have an increased resistance to antimicrobials and host defenses.